An auto-choke has been used to improve startability of an engine. A hot wax type auto-choke is known as such an auto-choke. This hot wax type auto-choke comprises a heater in wax, and the wax is expanded/contracted by ON/OFF operation of the heater so that a valve is opened/closed gradually in response to the expansion/contraction of the wax. Such a hot wax type auto-choke is provided in a bypass passage, which is provided, for example, additionally in a throttle body of a fuel injection engine, and adapted to open a valve at starting of the engine prior to warming up to increase the amount of intake air for the enhancement of startability.
FIG. 4 is a block diagram of a conventional hot wax type auto-choke control device.
In an engine control unit (ECU) 51 mounted to a vehicle is provided a control circuit 52 constituting a CPU such as a microcomputer, which is connected to a heater 54 of the auto-choke through a drive circuit 53. In the ECU 51 is provided a power circuit 57 connected to a battery 56 through a main switch 55. The power circuit 57 supplies a drive power from the battery 56 to the control circuit 52 and other electronic control parts or electric circuits and the like when the main switch 55 is turned ON.
Between the heater 54 and the battery 56 is connected a thermostat (engine temperature switch) 58 being set ON/OFF in response to the engine temperature, by which energization from the battery 56 to the heater 54 is ON/OFF in response to the engine temperature.
The heater 54, when energized (at the time of ON), expands the wax, causing a valve to be closed and volume increase of intake air to be shut off, and when energization is shut off (at the time of OFF), contracts the wax, causing the valve to be opened and the amount of intake air is increased.
In such an auto-choke described above, before engine starting, the heater 54 is in an OFF state and the valve of the auto-choke is opened.
If the main switch 55 is turned ON at the time of engine starting, a power source voltage is supplied to the control circuit 52. At this time, with the heater 54 kept in an OFF state and the valve opened, the amount of intake air is increased to enhance startability. When the engine is started, the control circuit 52 sets the heater 54 ON through the drive circuit 53 to close the valve gradually to thereby shut off volume increase of intake air, and performs fuel injection by ordinary running control. When the engine temperature is raised as a result of engine operation, the thermostat 58 is set ON.
Here, if after the main switch 55 is turned OFF to stop the engine, the main switch 55 is turned ON again to start the engine while the engine temperature is high, the heater 54 remains ON because of the thermostat 58 being ON, so that the valve of the auto-choke is kept closed without volume increase of intake air and engine starting at high temperature can be performed smoothly (without the thermostat 58, when the main switch is OFF, the heater 54 is also set OFF and the valve is kept open at the time of restarting at high temperature, so that the amount of intake air is increased in spite of high engine temperature, worsening startability).
However, in the conventional auto-choke control device, a special thermostat is required for the start control of an engine at the time of restarting at high temperature and the thermostat is mounted to a body separate from an ECU, so that the number of parts is increased, resulting in a restriction on layout and raising costs.
In view of the foregoing, an object of this invention is to provide an auto-choke control device capable of maintaining a good startability at the time of restarting at high temperature with a simple construction and without need of using a thermostat specific for an auto-choke, and preventing cost increase.